A common method practiced by the inventor for slitting and sealing two plastic films involves using heated knives to slit the films and thereafter seal the edges of the films together. Typically, the films used are a blown coextruded film and a lamination. Coextruded films are useful because multiple materials, having desirable properties, can be combined into one film. Similarly, laminations provide a method of combining dissimilar materials into one composite that cannot be combined by other methods such as coextrusion. The lamination typically comprises a nylon layer and a polyethylene layer, with a metallized polyester layer therebetween. The lamination and the coextruded film are fed from independent unwind rolls to a grooved mandrel, one film being layered and co-wound over the other. The conventional method practiced has been to layer the lamination closest to the heated knives, with the nylon layer of the lamination being positioned closest to the knives. The lamination engages the heated knives first because the melting point of the nylon and polyester is high enough to prevent sticking and subsequent polymer buildup on the knives. The heated knives slice into the mandrel grooves, engaging the lamination first, and thereafter slitting the lamination and the coextruded film. The heat energy from the knives fuses the two films together at the slit edges thereby forming a composite.
The rate at which the films are slit and sealed depends in significant part on the energy absorbing capability of the film materials. Using the above-described method achieves slitting and sealing rates of 50 feet of composite per minute. Generally, films that absorb energy efficiently will fuse and seal more readily. Accordingly, any method that maximizes energy transfer and facilitates the fusing process will improve the slitting and sealing rate.
There are also known in the art methods for slitting and sealing two or more materials using light beams from a laser instead of heated knives. Because light beams generated by lasers are more precise energy transfer devices than heated knives, laser-based methods typically result in cleaner seals where fusing is involved. One example of a laser slitting and sealing method is found in U.S. Pat. Nos. 4,414,051 and 4,490,203 to Bose, disclosing a method whereby a laser beam slits and seals an extrusion blown tube into two or more tubes. The Bose patents focus on reduced bead formation at slit/seal points and improved seal strength. Other laser slitting and sealing methods include: U.S. Pat. No. 5,630,308 to Guckenberger, disclosing a method of laser scoring packaging substrates to form an easy opening tear control package such as a pouch; U.S. Pat. Nos. 5,502,292 and 5,500,503 to Pernicka, et al., disclosing a method of simultaneously cutting and welding ultra thin metallic foil materials using a pulsed laser; and U.S. Pat. Nos. 5,314,767 and 5,455,129 to Bussard, disclosing a holographic product having sealed edges. In Bussard, a plastic top layer of the holographic product can be simultaneously cut and sealed with a variety of cutting tools including a laser.
While the prior art discloses methods for cutting and sealing materials using heated knives and lasers, it does not provide a method that focuses on a technique to improve slitting and sealing rates. Improved slitting and sealing rates result in higher composite output and reduced production costs. Accordingly, there is a need in the art for a more efficient slitting and sealing method that improves slitting and sealing rates.